1. Field of the Invention
The present invention relates to an active-matrix display apparatus employing light emitting devices such as organic EL (Electro Luminescence) devices which are each included in a pixel circuit and also relates to a driving method of the active-matrix display apparatus. To put it in more detail, the present invention relates to improvements of a technology for fixing defects of an image displayed by the active-matrix display apparatus. The present invention also relates to an electronic instrument which employs the active-matrix display apparatus.
2. Description of the Related Art
As a contemporary planar display apparatus, an organic EL display apparatus draws attention. This organic EL display apparatus employs self-light-emitting devices which are each included in a pixel circuit. Thus, the organic EL display apparatus can be designed as an apparatus which offers a wide viewing angle, requires no backlight and has a small thickness. In addition, since the organic EL display apparatus does not require a backlight, the power consumption of the apparatus can be reduced by the apparatus. On top of that, the organic EL display apparatus offers a high response speed.
The organic EL display apparatus employs organic EL devices laid out to form a two-dimensional matrix. Each of the organic EL devices is made of an organic light emitting layer which has a light emitting function. The organic light emitting layer is provided over a substrate and sandwiched between the anode and cathode electrodes of the organic EL device.
In a process of creating the organic EL device, infinitesimal foreign things and the like, which are floating in the air, may be stuck between the anode and cathode electrodes of the organic EL device, resulting in a short-circuit defect which makes the organic EL device incapable of emitting light. The short-circuit defect making the organic EL device incapable of emitting light is recognized as a death-point fault. A technology for fixing an organic EL device having such a death-point fault has been developed in development activities which started in the past. Such a technology is disclosed in materials such as Japanese Patent Laid-Open No. 2008-065200 (hereinafter referred to as Patent Document 1).
The active-matrix display apparatus disclosed in Patent Document 1 employs scan lines, signal lines and pixel circuits laid out to form a two-dimensional matrix. Each used for supplying a control signal to the pixel circuits, the scan lines each form a row of the two-dimensional matrix. Each used for supplying a video signal to the pixel circuits, the signal lines each form a column of the two-dimensional matrix. Each of the pixel circuits is located at the intersection of one of the scan lines and one of the signal lines. The scan lines, the signal lines and the pixel circuits are formed on a substrate. Every pixel circuit has a signal sampling transistor for sampling a video signal with a timing determined by the control signal. In addition, every pixel circuit has a device driving transistor for generating a driving current with a magnitude according to the video signal sampled by the signal sampling transistor. On top of that, every pixel circuit has a light emitting device for receiving the driving current from the device driving transistor and emitting light at a luminance level according to the driving current. That is to say, the light emitting device emits light at a luminance level according to the video signal which has been sampled by the signal sampling transistor. The light emitting device is a thin-film device having two terminals. That is to say, the light emitting device has a pair of electrodes which are referred to as an anode and a cathode. In addition, the light emitting device also includes a light emitting layer which is sandwiched by the anode and the cathode. At least one of the two electrodes are divided into a plurality of portions so that the light emitting device itself is virtually divided into a plurality of light emitting sub-devices. The light emitting sub-devices receive the driving current from the device driving transistor and, as a whole, emit light at a luminance level according to the driving current. Since the magnitude of the driving current is determined by the magnitude of the video signal sampled by the signal sampling transistor, as a whole, the light emitting sub-devices emit light at a luminance level according to the video signal. If one of the light emitting sub-devices is defective, this defective light emitting sub-device is electrically disconnected from the pixel circuit and the driving current is supplied to the remaining light emitting sub-devices. Thus, the remaining light emitting sub-devices are capable of sustaining the process of emitting light at a luminance level according to the video signal.
In the case of the active-matrix display apparatus disclosed in Patent Document 1, the light emitting device employed in every pixel circuit is divided into a plurality of light emitting sub-devices in advance. For example, the light emitting device employed in every pixel circuit is divided into a pair of light emitting sub-devices in advance. If one of the two light emitting sub-devices has a short-circuit defect, the defective light emitting sub-device is electrically disconnected from the pixel circuit. In this way, the pixel circuit having the death-point fault can be fixed. The probability that both the light emitting sub-devices become short-circuit defective at the same time is extremely low. Both the light emitting sub-devices become short-circuit defective at the same time because, for example, a foreign thing or the like is stuck on both the light emitting sub-devices.
Normally, only one of the two light emitting sub-devices becomes short-circuit defective. If the two light emitting sub-devices are kept as they are, however, the flowing driving current will be concentrated on the light emitting sub-device which has become short-circuit defective. Thus, both the light emitting sub-devices do not emit light so that a death-point fault is generated in the pixel circuit which employs the light emitting sub-devices. In order to solve this problem, the light emitting sub-device becoming short-circuit defective is electrically disconnected from the pixel circuit employing the defective light emitting sub-device and the driving current is supplied to the remaining the light emitting sub-device. In this way, the pixel circuit having the death-point fault can be fixed.